A continuous distribution of sound energy, referred to as an “acoustic field”, may be used for a range of applications including parametric audio and the levitation of objects.
By defining one or more control points in space, the acoustic field can be controlled. Each point may be assigned a value equating to a desired amplitude at the control point. A physical two-dimensional array of transducers may then be controlled to create an acoustic field exhibiting the desired amplitude at the control points. This may be achieved by actuating the set of transducers as a phased array. Focusing the energy in the desired control point location implies the transducers are excited at different times such that the waves output from each arrive together.
To achieve this in a controlled manner, the output from each transducer must be determined at the desired location. To fully specify the required input signal to the transducers and the output signal in the air, the input and output signals are assumed to be close enough to monochromatic waves over short timescales to each be modeled as a monochromatic wave. Thus, the modeled signals consist of an unchanging sine wave that approximates the intended transducer input and output. Unchanging sine waves may be specified exactly by complex values. For a given input signal, the response of a point in air is given by dividing the output complex value (modelling the signal at the point in air) by the input complex value (modelling the signal input to the transducer). This assumes that the transducer may be modelled linearly. The map of such complex values or phasors through all space around the transducer may be described as a “transducer model”.
In order to create these effects above an interactive surface (which may comprise a visible screen) acoustic waves must be induced volumetrically in the space above the surface. This is problematic as existing screen and interactive surface technologies are not acoustically permeable. This leads to solutions in which integration with mid-air haptic technology extends only to placing a transducer array around the outer edge of the surface.
But this “active bezel” approach limits the level of acoustic control that can be obtained in the center of the surface. This problem becomes exaggerated as screen size increases. Further, the cost, bulk and added complexity of creating an array around the edge of a surface are all problems that limit the uptake and scope of mid-air haptic technology.
It would therefore be commercially advantageous to ameliorate or eliminate these obstacles by designing screen technologies with structures that allow this haptic-based functionality.
Furthermore, many in-air transducers that could be used to create an acoustic field exhibiting the desired amplitude at the control points are available as off-the-shelf components. Because the primary purpose of these components is range finding, they often have little or no calibration. This means that while often such devices have a polarity (that is, depending on which way they are connected their phasor response may be inverted unintentionally), the polarity is not marked or indicated on the electronic component. Thus, individual calibration of such devices may be necessary. Further, in all transducers, even those produced specifically for this use case, small deviations in the offset of the complex phasor from the input signal is not addressed. This can differ on a transducer-to-transducer basis and require a per-unit calibration. This may include variations in amplitude across devices, as again compensation for such differences are unnecessary when considering the range finding use case.
For each type of transducer, an average “transducer model” describing the phasor distribution in space may be produced describing the output signal at the carrier frequency in the air at a known spatial offset from an averaged transducer. Individual manufacturing variation, however, may cause deviations from this idealized model. This may be due to a variety of factors, including manufacturing tolerance errors in the placement of the individual transducer elements, and/or added covering materials that may modify both the phase and amplitude parts of the phasor. The application of simple modifications to the behavior of the model in software may be used to account for and correct such variations.
Further, all components have limited lifespans. Phased array systems may have potentially hundreds or even thousands of individual transducer elements, many of which will likely fail before the product incorporating the transducers reaches end-of-life. If the calibration can detect such failed, failing or out-of-specification transducers, the transducer array may function at peak performance by working around the missing or incorrect transducer output. Since having a per-device calibration step is an extra expense, any methods of simplifying or automating any such step is of commercial value.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.